/Engine/Source/Runtime/Engine/Classes/Camera/PlayerCameraManager.h
Event triggered upon the start of a multi-part photograph capture (i.e. a stereoscopic or 360-degree shot). This is an ideal time to turn off rendering effects that tile badly (UI, subtitles, vignette, very aggressive bloom, etc; most of these are automatically disabled when r.Photography.AutoPostprocess is 1).
void OnPhotographyMultiPartCaptureStart()